Thermoplastics may be melt spun at exceptionally high speeds, while maintaining desirable properties that are obtained at lower spinning speeds, by adding a small amount of a liquid crystalline polymer containing repeat units derived from specified monomers.
Fibers made from thermoplastics, both natural and synthetic, are important items of commerce. These fibers are used for apparel, luggage, thread, and industrial uses. Oftentimes these fibers are formed by melt spinning, that is by melting the thermoplastic, forcing (extruding) the molten polymer through a small orifice (spinneret), cooling, and then using that extrudate, perhaps after having undergone other treatments such as drawing, as a fiber, see for example H. Mark, et al., Ed., Encyclopedia of Polymer Science and Engineering, Vol. 6, John Wiley and Sons, New York, 1986, p. 802-839, and W. Gerhartz, et al., Ed., Ullmann""s Encyclopedia of Industrial Chemistry, 5th Ed., Vol. A10, VCH Verlagsgesellschaft mbH, Weinheim, 1987, p. 511-566. Many important types of fibers are spun in this way, for example polyesters, polyamides (nylons), and polyolefins.
Melt spinning technology is relatively mature, and in recent years improvements have centered around producing higher quality more consistent fibers, and in improving the productivity of spinning equipment to lower spinning costs. One way to accomplish the latter is to increase spinning speeds, i.e., increase the length of fiber produced per unit time at constant dpf through a spinneret hole. This has been accomplished partly by improving the spinning machines themselves, for example by modifying the windup part of the machines to increase the speed at which the fiber can be wound onto a bobbin. Very high windup speeds (WUS), for example 6,000 m/minute, can be obtained on some spinning machines.
However, it has been found that often when fiber is spun at very high speeds, the properties of the fiber are different from those of fibers spun at lower speeds. In many cases the properties of the fiber spun at high speed are poorer for certain uses than those spun at lower speeds, and so the spinning speed may be limited not by equipment limitations, but on the properties needed in the fiber obtained. Therefore methods of obtaining higher WUS (which is the actual speed of production of the fiber) without substantially deleteriously affecting the fiber properties are desired.
The effects of changing spinning speeds are varied. For instance in U.S. Pat. No. 4,442,057 at column 1, lines 7-33, to it is stated
xe2x80x9cSome preliminary molecular orientation is induced in the fibers during melt spinning and this is increased by drawing to the degree required for any given fiber product. Drawing may be operated as a completely separate process after winding up and storing spun filaments or it may immediately follow spinning by forwarding spun filaments directly at controlled speed to a drawing process without interruption, or it may be still more closely integrated with spinning by omitting even intermediate speed control between spinning and drawing as for example in British Pat. No. 1,487,843.
Increasing the spinning speed increases the production rate but also increases the preliminary orientation thereby reducing the extensibility of the filaments and the extent to which they can be drawn. This has various disadvantages in different contexts. In certain speed ranges it can result in unacceptable product variability at otherwise practicable speeds: in processes aimed at very high tenacity filaments it can reduce the tenacity achievable: and in spin-lag-draw processes the reduction in subsequent draw ratio reduces the decitex required at spinning, partially offsetting the production rate advantage of the higher spinning speed. Various means have been proposed to mitigate these disadvantages in the manufacture of fibers of polyethylene terephthalate by suppressing the preliminary orientation induced at spinning.xe2x80x9d
Higher WUS also can lead to shorter elongations to break, higher tensile modulus at lower elongations (say 50 or 100%), any or all of which are disadvantageous in some applications.
U.S. Pat. No. 4,442,057 describes the addition of small amounts of liquid crystalline polymers (LCP) to thermoplastics to allow high speed fiber spinning while maintaining desirable polymer properties. LCPs of the composition described herein are not mentioned.
U.S. Pat. No. 4,518,744 describes the use of various polymers as additives in thermoplastics to allow high speed fiber spinning while maintaining desirable polymer properties. LCPs are not mentioned in this patent.
European Patent Application 80,273 describes the use of thermoplastic blends with other polymers, including LCPs, to make bulked fibers using melt spinning. The LCPs described herein are not mentioned.
U.S. Pat. No. 5,525,700 describes certain liquid crystalline polymer compositions, some of which are used herein. However fiber spinning is not mentioned in this patent.
This invention concerns a process for the melt spinning of one or more thermoplastics at windup speeds of about 1000 m/minute or more, wherein the improvement comprises, spinning said thermoplastic or thermoplastics as a blend which contains about 0.1 to about 10 percent by weight of a liquid crystalline polymer, said percentage based on a total amount of said thermoplastic or thermoplastics plus said liquid crystalline present,
and provided that said liquid crystalline polymer consists essentially of repeat units of the formula:
(I) at least one repeat unit selected from the group consisting of 
(III) at least one repeat unit selected from the group consisting of 
xe2x80x83wherein:
a molar ratio of (II) to (III) ranges from about 25:75 to about 90:10;
a molar ratio of (I) to [(II)+(III)] is substantially 1:1;
a molar ratio of (IV) to (V) ranges from about 97:3 to about 50:50;
a number of moles of (IV) plus (V) ranges from about 100 to about 600 per 100 moles of (I); and
wherein (I), (II), (III), (IV), (V) and (VI) are in units of moles.
Throughout this Application the number of moles of (I) is the total moles of (IA) plus (IB) plus (IC) and the total number of moles of (III) is the total moles of (IIIA) plus (IIIB).
This invention also concerns a composition, comprising:
(a) from about 99.9 to about 90 percent by weight of a thermoplastic;
(b) from about 0.1 to about 10 percent by weight of a liquid crystalline polymer consisting essentially of repeat units of the formula:
(I) at least one repeat unit selected from the group consisting of 
(III) at least one repeat unit selected from the group consisting of 
xe2x80x83wherein:
a molar ratio of (II) to (III) ranges from about 25:75 to about 90:10;
a molar ratio of (I) to [(II)+(III)] is substantially 1:1;
a molar ratio of (IV) to (V) ranges from about 97:3 to about 50:50;
a number of moles of (IV) plus (V) ranges from about 100 to about 600 per 100 moles of (I); and
wherein (I), (II), (III), (IV), (V) and (VI) are in units of moles, and said percent by weight of (a) and said percent by weight of (b) are based on the total amount of (a) and (b) present.